1. Field of the Invention
The present invention relates to a method and apparatus for making an iron silicide film, a method and apparatus for making an photoelectric transducer, and a method and apparatus for making a photoelectric transducer unit.
2. Related Background Art
In recent years, compound semiconductors have widely been used in various optical devices, electronic devices, other devices, and the like. Among them, silicide semiconductors have been developed vigorously as materials which can exhibit excellent electric, optical, magnetic, and thermoelectric characteristics due to their complicated and diversified combining modes. Examples of silicide semiconductors include transitional metal silicide semiconductors typified by iron silicide, and alkaline earth silicide semiconductors typified by calcium silicide and magnesium silicide. In particular, attention has been focused on iron silicide as a material which is quite usable in practice and less influential on environments, since its constituent elements are iron and silicon which exhibit a low environmental load and a long resource life, its lattice mismatching with a typically employed silicon substrate is less, and so forth.
In general, iron silicide which is expressed by FexSiy exhibits a plurality of crystal phases depending on its growth condition and the composition ratio (x:y) between iron and silicon atoms. In crystalline iron silicide, only β-FeSi2 has been known to have a semiconductor characteristic. β-FeSi2 directly has a bandgap (where Eg is about 1.85 eV) in a 1.55-μm band as an optical communication wavelength. Using its heterojunction with a silicon layer, LED and PD which can emit light at room temperature have been developed. Also, since β-FeSi2 is less influential on environments as mentioned above, and has a bandgap different from that of crystalline silicon and amorphous silicon while exhibiting a relatively large absorption coefficient for light having a long wavelength, it is useful as an i layer of a p-i-n junction constituting a photoelectric transducer.
Various techniques have been proposed for β-FeSi2 and its forming methods. Examples of typical techniques include SPE (Solid Phase Epitaxy), RDE (Reactive Deposition Epitaxy), IBS (Ion Beam Synthesis), MBE (Molecular Beam Epitaxy), PLD (Pulsed Laser Deposition), and MOCVD (Metal organic Chemical Vapor Deposition).
Specifically, SPE and RDE are methods in which elementary iron or iron silicide is deposited onto a silicon substrate and then is heated to 500° C. or higher, or iron is deposited onto a substrate at a temperature of 400° C. or higher, so as to form the aimed compound by a solid-phase reaction between iron and silicon. More specifically, a method in which silicide is deposited by PVD onto a substrate at a temperature of 200° C. to 600° C. and then is annealed at a temperature of 500° C. to 900° C. (see Japanese Patent Application Laid-Open No. HEI 4-210463), a method in which iron is deposited by PVD onto a substrate at a temperature of 625° C. to 725° C. and then is annealed at a temperature of 625° C. to 725° C. for 60 minutes (see Japanese Patent Application Laid-Open No. HEI 7-166323), and a method in which silicide is formed at a substrate temperature of 400° C. to 700° C. (550° C. to 650° C. in examples) by sputtering using a krypton or xenon gas (see Japanese Patent Application Laid-Open No. 2001-64099) have been proposed.
MOCVD is a kind of thermal CVD using a mixed gas formed by an iron-containing organic gas such as ferrocene or iron carbonyl and a silicon-atom-containing gas. More specifically, a method forming iron silicide at a substrate temperature of 500° C. by using a mixed gas of iron pentacarbonyl and monosilane has been proposed (see Japanese Patent Application Laid-Open No. 2002-47569).
IBS is a method in which a substrate is irradiated with ion beams of elements or compounds constituting a material, so as to deposit silicide thereon, and can form silicide by processing at a relatively low temperature. More specifically, a method in which a silicon substrate heated at 300° C. is alternately irradiated with iron and silicon ion beams, so as to form iron silicide has been proposed (see Japanese Patent. Application Laid-Open No. HEI 10-130826). PLD is a film-forming method using laser abrasion with pulse laser adapted to yield a high output, and can form silicide by processing at a relatively low temperature. More specifically, a method in which iron silicide is formed by using ArF excimer laser at a substrate temperature of 100° C. to 400° C. has been proposed (Japanese Patent Application Laid-Open No. 2000-178713).